In a split decision, the high court sided with 10 death row inmates who argued that, under Arkansas' constitution, only the Legislature can set execution policy. Legislators in 2009 voted to give that authority to the Department of Correction.

The 2009 law says a death sentence is to be carried out by lethal injection of one or more chemicals that the director of the Department of Correction chooses.

Death row inmate Jack Harold Jones Jr. sued the head of the correction department in 2010, challenging the constitutionality of the law. Nine other inmates have since joined the suit, asking that the law be struck down.

The state, meanwhile, asked the court to free up several executions it halted because of this lawsuit.

It wasn't immediately clear what the court's ruling will mean for the 40 men on death row in Arkansas. There aren't any pending executions, and the state hasn't put anyone to death since 2005, in part because of legal challenges like this one.

Three Arkansas inmates who were scheduled to be put to death last summer were spared by the state Supreme Court almost exactly a year ago. Jason Farrell McGehee, Bruce Earl Ward, and Marcel Wayne Williams, all of whom are plaintiffs in the lethal injection lawsuit, received stays of executions from the high court on June 23, 2011, according to ArkansasNews.com.

Josh Lee, an attorney for the death row inmates who challenged the law, declined to comment Friday.

During oral arguments last week, Lee said the state would have two options if the court found the law unconstitutional.

"The Legislature could either choose to stick with the 1983 statute, which everybody concedes is constitutional, or the Legislature could decide we want to amend it," Lee said last week.

The state adopted lethal injection as its method of capital punishment in 1983. There have been legal challenges to the way the state kills its condemned prisoners since then. In 2009, in the midst of a legal battle over lethal injection, the state Legislature passed the law that the court struck down Friday.

Joseph Cordi, an attorney for the state, told the Supreme Court last week that he thought the state would be left with the earlier law if the court struck down the entire statute.

Part of the 2009 law also says that in the event it's found unconstitutional, death sentences will be carried out by electrocution.

"That would be up for the lawyers to untangle and figure out what it means, but that's a possibility," prisons spokeswoman Dina Tyler said.

Since the reinstatement of capital punishment by the U.S. Supreme Court in 1976, Arkansas has been the only state to ever conduct three executions on the same night, according to The Death Penalty Information Center, a non-profit organization. Triple executions were done twice in Arkansas's history: first on Aug. 3, 1994, under Gov. Jim Guy Tucker, and then again on Jan. 8, 1997, under Gov. Mike Huckabee, records on DeathPenaltyInfo.org show.